Foldable cover and display for an electronic device

ABSTRACT

Electronic devices including a display layer and a cover layer including a foldable region are disclosed herein. The display layer and the cover layer are configured to be moved between a folded configuration and an unfolded configuration by bending the cover layer along the foldable region. Methods of making a cover layer for an electronic device are also disclosed.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a continuation patent application of U.S. patentapplication Ser. No. 15/870,672, filed Jan. 12, 2018 and titled“Foldable Cover and Display for an Electronic Device,” which is anonprovisional patent application of and claims the benefit of U.S.Provisional Patent Application No. 62/453,014 filed Feb. 1, 2017 andtitled “Foldable Cover and Display for an Electronic Device,” thedisclosures of which are hereby incorporated herein by reference intheir entireties.

FIELD

The described embodiments relate generally to bendable or flexiblelayers for an electronic device. More particularly, the presentembodiments relate to bendable covers coupled to a display layer for anelectronic device.

BACKGROUND

Traditionally, electronic devices have a single form factor that may bedriven by the size and shape of the display. Because many traditionaldisplays are rigid or at least not flexible, a traditional device thatis adaptable to accommodate multiple form factors includes the use of amechanical hinge or pivot joint. However, these traditionalconfigurations used for traditional notebook and tablet devices areinherently limited by the integration and size required by a separatemechanical hinge.

Embodiments described herein are directed to devices and techniques forforming portable electronic devices having a flexible cover coupled to aflexible display that do not have the limitations or drawbacksassociated with some traditional solutions.

SUMMARY

Embodiments described herein relate to techniques for forming flexiblecover sheets. In particular, cover sheets may be formed to facilitatelocalized bending or flexing without producing unacceptable levels ofinternal stress. The embodiments described herein can be used tomanufacture cover sheets formed using glass, sapphire, or other ceramicmaterials.

Additional embodiments described herein relate to electronic devicesincluding flexible cover sheets. The electronic devices may furtherinclude a flexible display layer. An example electronic device comprisesa display layer and a cover layer coupled to the display layer anddefining a foldable region, wherein the display layer and the coverlayer are configured to be moved between a folded configuration and anunfolded configuration by bending the cover layer along the foldableregion. In embodiments, the foldable region of the cover layer comprisesa ceramic material, such as a glass, a metal oxide ceramic, or otherceramic material. In further embodiments, the ceramic material definesat least a portion of an exterior surface of the electronic device.

In some embodiments, the cover layer comprises a continuous layer of aceramic material. An exterior surface of the continuous layer of ceramicmaterial can define an exterior surface of the electronic device. Suchan arrangement can present an impact and/or scratch resistant surface toa user. An opposing interior surface of the continuous layer of ceramicmaterial can face the display layer.

In embodiments, the continuous layer of ceramic material has asubstantially uniform thickness. In some embodiments, the continuouslayer of ceramic material may be treated to modify the stress state inthe layer in order to facilitate folding of the layer. For example, thecontinuous layer of ceramic material may have a reduced stress conditionat an intermediate configuration, between the folded configuration andthe unfolded configuration of the electronic device. As another example,the continuous layer of ceramic material may be treated to reduce thetensile stresses in the layer in a folded configuration of the device ascompared to a conventional ceramic cover sheet in the same foldedconfiguration.

In additional embodiments, the continuous layer of ceramic material hasa variable thickness to facilitate folding of the layer. For example,the continuous layer incorporates one or more relief features on theexterior side, the interior side, or both sides of the layer in thefoldable region. A relief feature may provide a locally thinned regionof the continuous layer of ceramic material; the continuous layer ofceramic material may also be referred to as a substrate. The cover layermay further comprise a filler material disposed in the relief feature.

In embodiments, an electronic device comprises: a display; a substratecoupled to the display and having a foldable region including a relieffeature; and a filler disposed in the relief feature and optically indexmatched to the substrate, wherein the substrate is configured to movebetween a folded configuration and an unfolded configuration by foldingand unfolding the foldable region. An example cover layer comprises: asubstrate having an array of relief features formed into a surface ofthe substrate; and a filler disposed in the array of relief features andhaving an optical index that is index matched to the substrate.

In further embodiments, a laminate cover layer comprises a laminate of acontinuous layer of ceramic material combined with segments, panels orpanel layers of a different material. The continuous layer of ceramicmaterial may be of substantially uniform thickness or of variablethickness. In this arrangement, the continuous layer of ceramic materialmay be referred to as a base layer for the attached panels. The panelsmay be arranged over and affixed to an interior side of the continuouslayer, facing the display layer. In an example, the panels have a lowerstiffness than the continuous layer but have sufficient stiffness tosupport the continuous layer away from the foldable region. The panelsmay also have a greater thickness than the continuous layer to supportthe continuous layer and/or provide impact absorption. A set of panellayers may define a set of gaps. Gaps between the panels may be filledwith an additional material having a lower stiffness than the panels tofacilitate folding of the cover sheet. In some embodiments, a single gapbetween two panels defines the foldable region. In other embodiments,the foldable region includes one or more panels; the one or more panelsin the foldable region may have at least one dimension (e.g., lengthand/or width) that is smaller than panels outside the foldable region.

In embodiments, an electronic device comprises: a display and a laminatecover layer coupled to the display and comprising: a ceramic base layer;a set of panel layers arranged over a surface of the ceramic base layerand defining a foldable region, wherein the display and the laminatecover layer are configured to be folded along the foldable region. Anexample laminate cover layer comprises: a ceramic base layer; a set ofpanel layers bonded to the ceramic base layer and defining a set ofgaps, each gap defined between an adjacent pair of panel layers of theset of panel layers; and a filler material disposed in the each of theset of gaps, the filler material being index matched to at least one ofthe ceramic base layer or the set of panel layers.

In additional embodiments, a laminate cover layer comprises a laminateof segments, panels, or panel layers of ceramic material combined with acontinuous layer of a different material. As an example, the segments ofceramic material may be combined with a continuous layer of a softermaterial, the continuous layer of the softer material being thicker thanthe segments of ceramic material. The continuous layer of the softermaterial may be referred to as the base layer and the panels of ceramicmaterial affixed to the outer side of the base layer. The inner side ofthis base layer faces the display layer. The foldable region may includeone or more panels; the one or more panels in the foldable region mayhave at least one dimension (e.g., length and/or width) that is smallerthan panels outside the foldable region.

In embodiments, an electronic device comprises: a display and a laminatecover layer coupled to the display and comprising: a base layer; a setof ceramic panel layers arranged over a surface of the base layer anddefining a foldable region, wherein the display and the laminate coverlayer are configured to be folded along the foldable region. An examplelaminate cover layer comprises: a base layer and a set of ceramic panellayers bonded to the base layer and defining a set of gaps, each gapdefined between an adjacent pair of ceramic panel layers of the set ofceramic panel layers. In further embodiments, the set of panel layers isat least partially embedded into the surface of the base layer, and aportion of the base layer fills gaps that are defined between adjacentpanel layers of the set of panel layers.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be readily understood by the following detaileddescription in conjunction with the accompanying drawings, wherein likereference numerals designate like elements.

FIGS. 1A and 1B respectively illustrate a device in open and closedconfigurations.

FIGS. 2A, 2B, and 2C respectively show cross-sectional views of a devicein folded, partially unfolded, and unfolded configurations.

FIGS. 3A, 3B, and 3C respectively show cross-sectional views of anotherdevice in folded, partially unfolded, and unfolded configurations.

FIGS. 4A, 4B, and 4C respectively show cross-sectional views of anotherdevice in folded, partially unfolded, and unfolded configurations.

FIGS. 5A, 5B, and 5C respectively show cross-sectional views of anotherdevice in folded, partially unfolded, and unfolded configurations.

FIG. 6A illustrates a side view of a sheet component preformed to apreliminary shape and annealed.

FIG. 6B shows the sheet component of FIG. 6A in a folded position.

FIG. 6C shows the sheet component of FIG. 6A in an unfolded position.

FIG. 7A illustrates a side view of another sheet component preformed toanother preliminary shape and annealed.

FIG. 7B shows the sheet component of FIG. 7A in a folded position.

FIG. 7C shows the sheet component of FIG. 7A in an unfolded position.

FIGS. 8A, 8B, and 8C illustrate alternate bend shapes for a preformedsheet component.

FIGS. 9A, 9B, and 9C illustrate formation of a bend in a sheet componentusing a pair of plates; the sheet component is shown from the side.

FIGS. 10A, 10B, 10C, and 10D illustrate formation of a bend in a sheetcomponent using a mandrel; the sheet component is shown from the side.

FIGS. 11A and 11B illustrate formation of a bend in a sheet componentusing adjustable rollers; the sheet component is shown from the side.

FIG. 12A illustrates a preliminary shape of a sheet component.

FIG. 12B illustrates an adjustment of the shape of FIG. 12A to a tighterbend radius before strengthening.

FIG. 12C illustrates an unfolded configuration of the sheet component ofFIGS. 12A and 12B.

FIG. 13 illustrates an example cross-sectional view of a cover sheetcoupled to a display layer using a cladding layer.

FIG. 14A illustrates an example cover sheet having a single relieffeature.

FIG. 14B illustrates an example cover sheet having multiple relieffeatures.

FIG. 14C illustrates an example electronic device in a folded portion,the electronic device including a cover sheet having a single relieffeature and a flexible display layer.

FIGS. 15A and 15B illustrate example cover sheets having an array ofrelief features formed on two sides of a substrate.

FIG. 16 illustrates an example cover sheet having two asymmetrical setsof relief features formed on two sides of a substrate.

FIGS. 17A and 17B illustrate an unfolded and folded state of an examplecover sheet having relief features.

FIGS. 18A and 18B illustrate an unfolded and folded state of an examplecover sheet having two sets of relief features.

FIGS. 19A and 19B illustrate an unfolded and folded state of anotherexample cover sheet having two sets of relief features.

FIGS. 20A and 20B depict example cover sheets formed from a laminatedstack of layers.

FIG. 20C illustrates an example electronic device in a folded portion,the electronic device including a laminate cover sheet and a flexibledisplay layer.

FIGS. 21A and 21B depict example cover sheets having multiple panelsintegrated with a flexible substrate.

FIG. 21C illustrates an example electronic device in a folded portion,the electronic device including another laminate cover sheet and aflexible display layer.

FIG. 22 illustrates a cross-sectional view of a sheet component with alocally thinned region which has been chemically strengthened.

FIG. 23 illustrates masking of the locally thinned regions of the sheetcomponent shown in FIG. 22.

FIGS. 24A and 24B illustrate strengthening of different sides of a sheetcomponent to different depths.

FIG. 25 is a flowchart providing an example of a method for producing achemically strengthened preformed cover glass.

FIG. 26 shows a block diagram of components of an electronic device.

The use of cross-hatching or shading in the accompanying figures isgenerally provided to clarify the boundaries between adjacent elementsand also to facilitate legibility of the figures. Accordingly, neitherthe presence nor the absence of cross-hatching or shading conveys orindicates any preference or requirement for particular materials,material properties, element proportions, element dimensions,commonalities of similarly illustrated elements, or any othercharacteristic, attribute, or property for any element illustrated inthe accompanying figures.

Additionally, it should be understood that the proportions anddimensions (either relative or absolute) of the various features andelements (and collections and groupings thereof) and the boundaries,separations, and positional relationships presented therebetween, areprovided in the accompanying figures merely to facilitate anunderstanding of the various embodiments described herein and,accordingly, may not necessarily be presented or illustrated to scale,and are not intended to indicate any preference or requirement for anillustrated embodiment to the exclusion of embodiments described withreference thereto.

DETAILED DESCRIPTION

The following disclosure relates to electronic devices having a flexibleor bendable region. More specifically, the embodiments described hereinare directed to an electronic device having a display layer and a coverlayer that are configured to fold or bend along a flexible or bendableregion. The flexible cover layer may be formed from a ceramic material(e.g., glass, strengthened glass, sapphire, zirconia) to provide somemeasure of protection for the flexible display from impact or otherpotential damaging contact. The flexible cover layer may also providestructural support for the display along both the folded and non-foldedregions of the device. As used herein, a cover layer may also bereferred to as a cover sheet or simply as a cover.

In general, a foldable electronic device can be folded to accommodate avariety of form factors. For example, a foldable electronic device maybe used in an unfolded configuration to allow use of an entire displayarea. The foldable electronic device may also be used in a foldedconfiguration, which may have a more compact size and may also provide asmaller display area. As described in more detail below, a foldableelectronic device may be configured to allow multiple folds to providemultiple display arrangements for the electronic device. In some cases,the electronic device can be partially or wholly unfolded to adjust thesize of the viewable display area.

Example electronic devices include a display and a cover sheetpositioned over the display to provide protection and structural supportfor the display. The cover sheet may be generally referred to as a coverlayer and may include one or more glass or other ceramic layers. Thedisplay may be generally referred to herein as a display layer, whichmay include various elements that are configured to produce a dynamicvisual output. An example display layer may include a liquid crystaldisplay (LCD), an organic light emitting diode (OLED) display, an activelayer organic light emitting diode (AMOLED) display, an electrophoretic(electronic ink) display, or other similar type of display components.In some embodiments, the display layer may be coupled to the cover layerusing an adhesive layer, cladding layer, or other bonding agent. Theelectronic device may also include one or more additional deviceelements that are coupled to the display layer and cover layer. Asdescribed in more detail herein, the additional device elements mayinclude a battery, circuit boards, circuit substrates, backing layers,and/or housing elements.

The display may be configured to bend or fold along a flexible orbendable region of a foldable electronic device. Flexible displaysinclude, but are not limited to, thin film transistor (TFT) displays,LCD display, and OLED displays that are formed from one or more flexiblelayers. In particular, the display may include or be integrated withvarious layers, including, for example, a display element layer, displayelectrode layers, a touch sensor layer, a force sensing layer, and thelike, each of which may be formed using flexible substrates. Forexample, a flexible substrate may be formed from a polyimide, PEEK,Mylar or other similar type of material. The flexible substrate may haveone or more layers of conductive elements or traces that routeelectrical signals to electronic components positioned along theflexible substrate.

In some embodiments, information regarding configuration and/ororientation of the electronic device may be used to control the outputof the display. Example sensors include accelerometers, gyroscopes,magnetometers, and other similar types of position/orientation sensingdevices. Such information may be provided by one or more sensors thatare operably coupled to processing circuitry, which controls the displaybased on the sensor signals. For example, a portion of a display may beturned off, disabled, or put in a low energy state when the device istransitioned from an unfolded position to a folded configuration. Thismay be useful when a portion of the display is not visible on a part ofthe display when the device is in a folded or partially folded position.Similarly, the display may be adapted to display graphical output in arotated mode (e.g., from landscape to portrait mode) depending onwhether the device is in an unfolded or folded configuration, which maychange the overall aspect ratio of the viewable area of the display. Thedisplay output may also be re-oriented based on the changes inorientation of the device.

Example display and cover layers may include a foldable region that isconfigured to fold or bend about the region. In some embodiments, thedisplay and/or cover layers are configured to allow localized folding orbending such that the fold occurs over only a portion of the layer. Forexample, an arc length of the fold or bend may be less than a length orwidth of the display or cover layer. In some cases, a foldable region ispositioned between two non-folding regions. The non-folding regions mayhave a flat, arced, contoured or virtually any other type of shape.However, the non-folding regions may be generally configured to maintaina consistent or static geometric shape or form when the device is foldedand unfolded.

Several parameters can be used to describe the geometry of folds orbends in sheet components. In general, a fold or bend may becharacterized at least in part by the minimum radius of curvature asmeasured, for example, on the inside surface of the device element.Example radii of curvature include, but are not limited to, radii lessthan 25 mm, less than 15 mm, less than 10 mm, from 1 mm to 25 mm, from 2mm to 25 mm, from 1 mm to 10 mm, from 2 mm to 10 mm, from 2 mm to 7 mm,or from 5 mm to 15 mm. In addition to or as an alternative to describinga bend as having a radius of curvature, a bend or fold may be measuredor characterized as the distance between the endpoints of the fold orbend. In an example, the fold or bend can be characterized by a bendwidth, which may be measured between two points on the inner surface ofthe device when the device is in a folded configuration. Further, thefold or bend can also be characterized by an inclusive angle defined bythe bend. As an example, a portion or component of the device may befolded back onto a common plane or direction, which could be describedas a bend angle of about 180°. As an additional example, the bend anglein the folded configuration may be in the range from 135 degrees to 180degrees. As referred to herein, a bend axis is a virtual line thatdefines the center around which the device or component of the device isbent.

As described herein, a foldable electronic device may have a cover layerthat is coupled to a display layer or element. In general, a cover layermay be characterized as having two generally opposing sides or faces,with at least one edge joining the sides or faces. An inward facing sideof the cover may face the display, and an outward facing side of thecover may face a user in some configurations of the device. In addition,when a foldable region of the cover layer is folded or bent, one side ofcover layer forms the inner surface or portion of the folded/bent region(also referred to as the inside of the fold or bend) and the other sideof the cover layer forms the outer surface or portion of the folded/bentregion (also referred to as the outside of the fold or bend). The radiusof curvature and/or the bend width of the folded/bent region may bemeasured from the inside surface as illustrated in FIGS. 6A and 6B anddescribed below.

In some embodiments, a cover layer suitable for use with the electronicdevices disclosed herein includes one or more ceramic layers orsubstrates. The ceramic layers or substrates may have a substantiallyuniform thickness or may vary in thickness as illustrated in embodimentsdescribed herein. In some embodiments, the thickness of the ceramiclayer or substrate ranges from 25 μm to 400 μm. In additionalembodiments, the thickness of the ceramic layer or substrate is from 1μm to 20 μm, from 5 μm to 15 μm, or from 1 μm to 10 μm. As used herein,the terms “ceramic,” “ceramic material,” and “ceramic layer” may be usedto describe materials having both crystalline and amorphous inorganicmaterials. Example ceramics include, but are not limited to, metaloxide-based materials. Metal oxide-based materials include, but are notlimited to, silica-based materials (e.g., glasses such asaluminosilicate and borosilicate glasses), alumina-based materials(e.g., single-crystalline and polycrystalline sapphire), zirconia-basedmaterials, and mixed metal oxides such as spinel-based materials (e.g.,magnesium aluminum oxide). As used herein, ceramics do not include bulkmaterials that may be characterized as metals and metal alloys. However,a ceramic may include a metal or metal alloy as a constituent componentor applied to the surface of the ceramic. In some embodiments, theceramic layer or ceramic material is optically transparent. For example,the optical transmissivity of the ceramic layer or ceramic material isat least 90%. In some embodiments, the ceramic layer or ceramic materialis translucent or otherwise able to transmit or pass light. As examples,ceramic layers of substantially uniform thickness may have a thicknessthat is uniform to within +/−5% or +/−10%.

For a cover layer including a continuous ceramic layer, the electronicdevice may be folded so that the continuous ceramic layer is on theinside or the outside of a given fold. If the continuous ceramic layeris on the inside of a fold, the exterior surface of the continuousceramic layer will be on the inside of the fold. Conversely, if thecontinuous ceramic layer is on the outside of a fold, the exteriorsurface of the continuous ceramic layer will be on the outside of thefold. In either configuration, the ceramic layer may define an exteriorsurface of the electronic device over the fold or foldable region.

In some embodiments, a continuous ceramic layer may be treated to have areduced stress condition at an intermediate configuration, between thefolded configuration and the unfolded configuration of the electronicdevice. As an example, the foldable region of the continuous ceramiclayer may be treated so that a first portion of a foldable regionlocated at the inside of the fold in the folded configuration has afirst compressive stress in the folded configuration; a second portionof the foldable region located at the outside of the fold in the foldedconfiguration has a second compressive stress in the unfoldedconfiguration; the first portion has a third compressive stress in anintermediate configuration, between folded and unfolded configurations,that is less than the first compressive stress; and the second portionhas a fourth compressive stress in the intermediate configuration thatis less than the second compressive stress. In some cases, the first andsecond portions of the ceramic layer may have a minimum stress condition(whether tensile or compressive) when the ceramic layer is in theintermediate configuration, between the folded and unfoldedconfigurations. As a further example, the continuous ceramic layer maybe treated so that the maximum tensile stress in the ceramic layer whenthe ceramic layer is in the folded condition is at least 20%, 30%, or40% lower than an untreated equivalent ceramic layer in the foldedcondition.

In additional embodiments, a cover layer comprises a substratecomprising a continuous ceramic layer and relief features formed intothe substrate. As examples, a relief feature may have a depth that is atleast 10%, 20% or 30% of the substrate thickness. A relief feature mayprovide a locally thinned region that generally extends across thefoldable region. As examples, the minimum thickness of the continuouslayer in the locally thinned region may be 10%, 20%, 30% or 40% of thethickness away from the locally thinned region. In addition, a relieffeature may provide a locally thinned region that does not extend acrossthe foldable region. As an example, multiple relief features may incombination generally extend across the foldable region. Further, arelief feature may take the form of a notch-shaped feature located nearan edge of the foldable region; when the foldable region is in thefolded position, the relief feature may located at a corner or othertransition region of the bend.

In many embodiments, the cover layer includes a translucent ortransparent ceramic layer, and the relief features may be filled with afiller material that is optically index matched to the translucentsubstrate. For example, the filler material may have an optical index ofrefraction or an optical index of reflection that closely approximatesthat at the substrate under normal operating or use conditions. In someinstances, a filler material that is index matched may be characterizedas having an optical index (e.g., reflection, refraction) that issubstantially matched to that of the substrate or other nearby material.The substrate may comprise a ceramic material and the filler materialmay include a polymer having suitable optical properties for being indexmatched and suitable mechanical properties to provide strain reliefduring bending or folding. For example, the polymer may be an acrylateor a silicone polymer. The polymer may be an adhesive, such as anoptically clear adhesive, or a polymer other than an adhesive. Opticallyclear adhesives include, but are not limited to, acrylate-based andsilicone-based adhesives.

In additional embodiments, a cover layer comprises multiple layers. Forexample, the cover layer comprises a continuous ceramic outer layer andinner layer segments or panels bonded to the outer layer and defining agap between at least one pair of inner layer segments or panels, with afiller material being disposed in the gap. The inner layer(s) may be ofa material that is more pliable than the material of the outer layer.For example, the outer ceramic layer may be a glass, such as achemically strengthened glass, or an oxide ceramic. Suitable innerlayers for glass ceramic layers include polymer materials. Suitableinner layers for metal oxide ceramic layers include glasses, polymers orcombinations thereof. For example, the polymer may be an acrylate or asilicone polymer. Suitable materials for the filler material includeadhesive polymer materials, such as optically clear adhesives. Thefiller material may be selected to have an optical index of refractionthat is index matched or substantially matched to at least one of theouter layer and the outer layer. As an example, a thickness of thesegments or panels of the inner layer may be at least 125% of thethickness of the outer layer. In examples, the segments or panels of theinner layer have a thickness from two to ten times or two to five timesa thickness of the outer layer.

As another example, the cover layer comprises a continuous inner layerand ceramic outer layer segments or panels bonded to the outer layer anddefining a gap between at least one pair of the ceramic outer layersegments or panels. A set of the panels of the outer layer may define aset of gaps. The inner layer may be of a material that is more pliablethan the material of the outer layer. For example, the outer ceramiclayer may be a glass, such as a chemically strengthened glass, or anoxide ceramic. Suitable inner layers include polymer materials. Forexample, the polymer may be an acrylate or a silicone polymer. As anexample, a thickness of the inner layer may be at least 125% of athickness of the segments or panels of the outer layer. In examples, theinner layer has a thickness from two to ten times or two to five times athickness of the segments or panels of the outer layer.

These and other embodiments are discussed below with reference to FIGS.1A-26. However, those skilled in the art will readily appreciate thatthe detailed description given herein with respect to these figures isfor explanatory purposes only and should not be construed as limiting.

FIGS. 1A and 1B depict a simplified example of a foldable electronicdevice. FIG. 1A depicts the device 100 in an unfolded configuration andFIG. 1B depicts the device 100 in a folded configuration. The unfoldedconfiguration may be referred to as an open configuration and the foldedconfiguration may be referred to as a closed configuration. As describedwith respect to other examples provided herein, a device may includemultiple folds and may include more than two configurations (e.g.,folded, partially folded or unfolded, and unfolded).

As shown in FIG. 1A, the device 100 includes a display 120 that isviewable through a first side of the device 100. A cover 110 ispositioned over the display 120 and is generally formed from atranslucent or transparent material or substrate. The device 100 mayalso include a housing 130 that forms at least a portion of an exteriorsurface of the device 100. In some implementations, the housing 130 atleast partially surrounds the display 120. In some implementations, thehousing 130 forms a backing or backing layer along a back surface of thedisplay 120. In some cases, the housing 130 is optional or is integrallyformed with the display 120 and cover 110.

FIG. 1A depicts the device 100 in a flat or unfolded configuration. Inaccordance with embodiments described herein, the cover 110, display120, and optional housing 130 may be folded or bent into one or morefolded configurations. In general, the device 100 may operate in adifferent state or provide different functionality when folded andunfolded. In the example of FIGS. 1A and 1B, the device 100 may beoperated in an interactive mode when unfolded as shown in FIG. 1A andmay be in a standby, power saving, or off mode when in the foldedconfiguration shown in FIG. 1B.

As shown in FIG. 1B, the device may define various regions.Specifically, the device 100 may include a folded or foldable region101, which forms or defines an edge or side of the device 100 when thedevice is in the folded configuration, as shown in FIG. 1B. The foldedor foldable region 101 may extend between a first non-foldable region102 and a second non-foldable region 104. While the first and secondnon-foldable regions 102 and 104 are depicted as flat, it is notnecessary that they be flat or planar in shape. In general, the shape ofthe non-foldable regions 102 and 104 does not change or is substantiallystatic between the folded and unfolded configurations of the device 100.

In the example of FIGS. 1A and 1B, the display 120 and cover 110 are notexposed when the device 100 is in the folded configuration (as depictedin FIG. 1B). This may help protect the display 120 and the cover 110when the device is not in use and may be moved or transported. In analternative configuration, the device 100 may be folded or bent in anopposite manner resulting in the display 120 and cover 110 beingpositioned along an externally facing surface of the device 100 when thedevice is in the folded configuration. This may allow the user to viewand/or interact with the device 100 in the folded configuration.

FIGS. 2A-5C depict additional example configurations in which the deviceincludes one or more foldable regions. As depicted in the followingexamples, the device may include multiple folds or bends. Each fold orbend may be configured to fold in a particular direction and have aparticular bend radius. For example, when a device has two foldableregions, a first localized bend is formed in a first foldable region anda second localized bend is formed in a second foldable region. In someembodiments, a ratio of a first bend angle of the first localized bendto a second bend angle of the second localized bend is from 0.3 to 0.7.The ratio between multiple bend regions may allow the device to befolded over onto itself as depicted in the example of FIGS. 4A-4C and5A-5C. Additionally, the device may be configured to have multipleconfigurations including, for example, a folded configuration, one ormore partially unfolded/folded configurations, and an unfoldedconfiguration. While the unfolded configurations of the followingexamples are depicted as being flat, it is not necessary that the devicebe flat or planar in shape in an unfolded configuration.

The devices shown in FIGS. 2A-5C include a cover layer, a display layer,and a backing layer, each of which allows folding of the device in thefoldable region(s). Example cover layers include at least one coverlayer foldable region comprising a ceramic material. The ceramicmaterial at least partially defines an exterior surface of theelectronic device. As shown, the display layer and the backing layerextend across the foldable region and are sufficiently flexible togenerally conform to the shape of the cover layer in a foldedconfiguration of the device. The display layer and/or the backing layermay be generally flexible or may include a foldable region aligned withthe foldable region of the cover layer. The foldable region of thedisplay layer may be capable of presenting output to a user so that thedisplay is viewable over the fold or bend. Flexible display layers andbacking layers are described in more detail with respect to FIG. 26.

FIGS. 2A-2C are cross-sectional views of a device 200 having twoopposing bends to form an s-shaped folded configuration. As shown inFIGS. 2A-2C, the device 200 includes a cover layer 210, a display layer220, and a backing layer 230. The cover layer 210 may be formed from oneor more ceramic layers where at least one of the layers defines anexternal surface of the device 200. The cover layer 210 may be formedfrom a translucent or transparent material. In general, the displaylayer 220 may be viewable through sides or surfaces of the device 200having the cover layer 210 and not viewable though surfaces or side ofthe device 200 having the backing layer 230. While the followingexamples are provided with respect to a single-sided display device, thesame principles and embodiments may be extended to double- or dual-sideddisplay devices.

FIG. 2A depicts the device 200 in a fully folded or closedconfiguration. In the fully folded or closed configuration, roughly athird of the display layer 220 is viewable along a first region 281 ofthe device 200. The display layer 220 is also viewable along a firstfoldable region 201 of the device 200 located along the right edge, asshown in FIG. 2A. The cover layer 210 is on the exterior of the deviceon first region 281 and first foldable region 201. In the fully foldedor closed configuration, the display layer 220 is not viewable along thesecond region 282 and third region 283 because those regions are foldedover themselves with the display layer 220 facing inward. Also for thesecond region 282 and the third region 283, the cover layer 210 isgenerally protected.

As shown in FIG. 2A, a second foldable region 202 extends between thesecond region 282 and the third region 283. In this particular example,the second foldable region 202 has a larger bend radius than the firstfoldable region 201. The second foldable region 202 is also configuredto bend in an opposite direction than the first foldable region 201. Insome implementations, the shape or curvature of the second foldableregion 202 may be different from the shape or curvature of the firstfoldable region 201.

FIG. 2B depicts a partially unfolded (or partially folded) configurationof the device 200. The partially unfolded configuration may be formedafter the third region 283 is rotated as indicated to straighten orunfold the second foldable region 202. As shown in FIG. 2B, roughly athird of the display layer 220 remains viewable along a first region 281of the device 200. However, as shown in FIG. 2B, the second foldableregion 202 is in an unfolded state or configuration, which unfolds thethird region 283 away from the second region 282. In this state orconfiguration, roughly two thirds of the display layer 220 is viewablealong the bottom or opposite side of the device 200. A portion of thedisplay layer 220 also remains visible along the first foldable region201.

FIG. 2C depicts a fully unfolded state or configuration of the device200. As shown in FIG. 2C, the entire display layer 220 is viewable alonga single side of the device. As previously mentioned, while the device200 is depicted as being flat in the unfolded state or configuration, itis not necessary that the device have a perfectly flat or planar shapein the fully unfolded configuration.

With respect to each of the configurations of FIGS. 2A-2B, the device200 may be configured to operate in different modes for eachconfiguration. For example, the device 200 may be configured to adaptthe display layer 220 to only display information along portions orregions that are viewable to a user in a particular configuration. Thedevice 200 may be configured, for example, to display only a portion ora scaled display for configurations in which a reduced area is visible.The device 200 may also be configured to present different interfacesfor different viewable portions of the display layer 220 depending onwhether the portions are viewable on the front or back of the device200. FIG. 2B depicts an example of such a dual display configuration.

FIGS. 3A-3C are cross-sectional views of another such device 300 havingtwo opposing bends at different heights to form an s-shaped foldedconfiguration. As shown in FIGS. 3A-3C, the device 300 includes a coverlayer 310, a display layer 320, and a backing layer 330. Similar to theprevious example, the cover layer 310 may include one or moretranslucent or transparent ceramic layers that define an exteriorsurface of the device 300.

FIG. 3A depicts the device 300 in a fully folded or closedconfiguration. In the fully folded or closed configuration, roughlyone-third of the display layer 320 is viewable along a third region 383of the device 300. The display layer 320 is also viewable along a secondfoldable region 302 of the device 300 located along the left edge, asshown in FIG. 3A. The cover layer 310 is on the exterior of the deviceon the third region 383 and second foldable region 302. In the fullyfolded or closed configuration the display layer 320 is not viewablealong the first and second regions 381 and 382 and the first foldableregion 301; the cover layer 310 is generally protected in these regions.

As shown in FIG. 3A, the second foldable region 302 has a larger bendradius than the first foldable region 301. The second foldable region302 is also configured to bend in an opposite direction than the firstfoldable region 301.

FIG. 3B illustrates a partially unfolded configuration (or partiallyfolded) configuration of the device 300. The partially unfoldedconfiguration may be formed after the third region 383 is rotated asindicated to straighten or unfold second foldable region 302. As shownin FIG. 3B, roughly one-third of the display layer remains viewablealong third region 383 and second foldable region 302.

FIG. 3C depicts a fully unfolded configuration of the device 300. Asshown in FIG. 3C, the entire display layer 320 is viewable along asingle side of the device; as shown, this is the front side of thedevice. As previously mentioned, while the device 300 is depicted asbeing flat in the unfolded state, it is not necessary that the devicehave a perfectly flat or planar shape in the fully unfoldedconfiguration. As previously discussed for device 200, device 300 may beconfigured to operate in different modes for each configuration shown inFIGS. 3A-3B.

FIGS. 4A-4C show cross-sectional views of a device 400 having twoopposing bends which face each other in the fully folded configuration.As shown in FIGS. 4A-4C, the device 400 includes a cover layer 410, adisplay layer 420, and a backing layer 430. Similar to the previousexample, the cover layer 410 may include one or more translucent ortransparent ceramic layers that define an exterior surface of the device400.

FIG. 4A depicts the device 400 in a fully folded or closedconfiguration. In the fully folded or closed configuration, roughly twothirds of the display layer 420 is viewable along the first region 481and second region 482 of the device 400. The display layer 420 is alsoviewable along the first and second foldable regions 401, 402 of thedevice 400. The cover layer 410 is on the exterior of all regions of thedevice 400 except third region 483.

As shown in FIG. 4A, the first foldable region 401 has a smaller bendradius than the second foldable region 402, which allows first region481 to overlap third region 483. The first foldable region 401 isconfigured to bend in an opposite direction than the second foldableregion 402.

FIG. 4B illustrates a partially unfolded (or partially folded)configuration of the device 400. The partially unfolded configurationmay be formed after the first region 481 is rotated as indicated tostraighten or unfold second foldable region 402. As shown in FIG. 4B,roughly one-third of the display layer 420 is viewable from the top ofthe device 400 along third region 483. Roughly two thirds of the displaylayer 420 is viewable from the bottom of the device 400, including alongfirst and second regions 481 and 482 and first foldable region 401.

FIG. 4C depicts a fully unfolded configuration of the device 400. Asshown in FIG. 4C, the entire display layer 420 is visible along a singleside of the device; as shown, this is the back side of the device. Aspreviously mentioned, while the device 400 is depicted as being flat inthe unfolded configuration or state, it is not necessary that the devicehave a perfectly flat or planar shape in the fully unfoldedconfiguration. As previously discussed for devices 200 and 300, device400 may be configured to operate in different modes for eachconfiguration shown in FIGS. 4A-4B.

FIGS. 5A-5C show cross-sectional views of another device having twoopposing bends which face each other in the fully folded configuration.As shown in FIGS. 5A-5C, the device 500 includes a cover layer 510, adisplay layer 520, and a backing layer 530. Similar to the previousexample, the cover layer 510 may include one or more translucent ortransparent ceramic layers that define an exterior surface of the device500.

FIG. 5A depicts the device in a fully folded or closed configuration. Inthe fully folded or closed configuration, the display layer 520 is notviewable as the cover layer 510 is on the interior of the device. Thecover layer and display layer are therefore protected from abrasion inthis configuration.

As shown in FIG. 5A, the first foldable region 501 has a smaller bendradius than the second foldable region 502, which allows first region581 to overlap third region 583. The third region 583 overlaps thesecond region 582. The first foldable region 501 is configured to bendin an opposite direction than the second foldable region 502.

FIG. 5B illustrates a partially unfolded (or partially folded)configuration of the device 500. The partially unfolded configurationmay be formed after the first region 581 is rotated to straighten orunfold second foldable region 502. As shown in FIG. 5B, roughlyone-third of the display layer 520 is visible along first region 581 andfirst foldable region 501.

FIG. 5C illustrates an unfolded configuration after the third region 583is rotated as indicated. After the device 500 is fully unfolded as shownin FIG. 5C, the display layer 520 is now viewable along a single side ofthe device; as shown, this is the front side. As previously mentioned,while the device 500 is depicted as being flat in the unfolded state orconfiguration, it is not necessary that the device 500 have a perfectlyflat or planar shape in the fully unfolded configuration. As previouslydiscussed for devices 200-400, device 500 may be configured to operatein different modes for each configuration shown in FIGS. 5A-5B.

In general, a folding or bending of a flat component will result in achange in the stress state for at least a portion of the flat componentat temperatures where the folding/bending stress is not relievedquickly. A flat component that is initially unstressed in a flat statewill, when bent or folded, induce tensile stresses along an outerportion of the bend or fold and compressive stresses along an innerportion of the bend or fold. In general, the tensile or compressivestress induced by bending or folding a flat component depends on variousfactors including the bend angle or amount of bending that is induced atthe fold. The tensile or compressive stress also depends on thethickness of the component and the bend radius of curvature. For a givencomponent, the maximum tensile stress will increase as the thickness ofthe component increases, as the bend radius decreases, and/or as thebend angle is increased. In general, it may be desirable to keep thetensile stress below a particular threshold level, which may drive orlimit the amount of bending or the bend angle of the component. Thethreshold stress level may also determine or limit the thickness and/orthe bend radius of the component. The techniques described below withrespect to FIGS. 6-12 and 14A-21B may be used to create componentshaving an increased thickness, a decreased bend radius, and/or a largerbend angle than may be achieved using some traditional techniques.

In some embodiments, a sheet component for an electronic device ispre-shaped prior to incorporation in an electronic device to facilitatethe formation of a foldable or bendable region within the sheetcomponent. An example pre-shaping process includes preforming the sheetcomponent to a preliminary shape including a bend region and annealingthe sheet component. The pre-shaping process may further include achemical strengthening step. In some embodiments, the shape of thepre-shaped sheet component is influenced by each of the steps in thepre-shaping process. In additional embodiments, the preforming step hasthe most influence on the shape of the pre-shaped sheet component. Thesheet component may be used to form or may include a cover layer of anelectronic device.

Pre-shaping of the sheet component as described herein can significantlyreduce the level of tensile and compressive stresses induced by bendingthe sheet component to the folded or closed configuration of the device.For example, when a bend region in the pre-shaped sheet component is atleast partially incorporated into a bend in the folded or closedconfiguration of the device, the stress state of the bend in thepre-shaped sheet component can affect the stress state of the bend inthe folded or closed configuration of the device. In some cases, thepreformed and annealed sheet component is referred to as having zero orsubstantially zero stress. However, it is not necessary that thepre-shaped sheet component have zero residual stresses and may, in fact,be chemically strengthened to produce an outer layer that is in acompressive state or retain some stress due to thermal processing. Inembodiments, the amount of tensile and/or compressive stress in thepreformed and annealed sheet component is less than a correspondingtensile and/or compressive stress when the sheet component is in eithera folded or unfolded configuration.

In general, a preformed sheet component having a preliminary shape mayinclude a localized bend geometry that is configured to limit thetensile stresses in the sheet component when the electronic device isin, for example, a folded or closed configuration. In general, thetensile stresses in the sheet component in the folded or closedconfiguration may be less than those that would be present in a similarlayer in the folded or closed configuration which had not been preformedand annealed. For a given sheet component thickness, use of a preformedsheet component can allow a smaller radius of curvature or bend width tobe obtained without exceeding a threshold or safe stress level.Similarly, for a given radius of curvature or bend width, a thickersheet component can be used. In addition, preforming of the sheetcomponent can reduce the amount of “springback” force when the sheetcomponent is in a folded closed configuration.

In embodiments, the preliminary shape is different from the shapeassumed in either the open (unfolded) or the closed (folded)configurations of the sheet component. For example, the radius ofcurvature, bend angle and/or the bend width of the preliminary shape maybe different from that of the sheet component in either the folded orunfolded configuration. In some implementations, the preliminary shapemay be configured so that the sheet component is biased towards eitherthe open (unfolded) or the closed (folded) configuration.

For purposes of the following discussion, a preforming set of operationsis performed on a sheet component. The sheet component may be a coverlayer, a ceramic layer, a substrate and/or laminate having multiplelayers of the same or different materials. For example, the sheetcomponent may include one or more ceramic (e.g., glass) layers and mayinclude one or more coatings, cladding layers, fillers, and/ormaterials. The sheet component may also include one or more translucentor transparent layers or materials. For ease of reference, the term“sheet component” is used to generically refer to any of theseconfigurations.

In some embodiments, the sheet component is preformed to a preliminaryshape intermediate between the shapes of the layer in the open andclosed configurations of the device. For example, the sheet componentmay be preformed to a shape including a bend having a radius ofcurvature greater than or equal to that in the closed configurationand/or having a bend angle less than that in the closed configuration.In embodiments, a minimum radius of curvature of the preliminary shapemay be up to two times greater or up to four times greater than that ofthe sheet component in the closed configuration. In embodiments, a bendangle of the preliminary shape may be from 90 degrees to less than 180degrees, from 45 degrees to 135 degrees or from 90 degrees to 135degrees.

FIG. 6A illustrates an example shape of a preformed sheet component (acover layer, ceramic layer or a substrate) having a radius of curvaturegreater than that of the cover shape in the closed configuration. Inthis example, the sheet component 602 is formed into a preliminary shape(as shown) and then annealed to relieve stresses due to the formingoperation. As stated previously, the sheet component 602 may havesignificantly reduced or near zero stress after being annealed. Inaddition, the sheet component may be cooled gradually enough from theannealing temperature so as not to induce additional thermal stresses.For example, inorganic glass sheet components may be cooled gradually tothe strain point to limit thermal stresses.

In some cases, the sheet component 602 is chemically strengthenedsubsequent to annealing to induce compressive stress along the outerportions of the sheet component 602. When at least a portion of thefoldable region has been chemically strengthened, the combination of thestresses due to chemical strengthening and the stresses generated onfolding of the foldable region can determine the stress state of theglass in the foldable region. For example, the outer portion can have acompressive stress in the intermediate preformed configuration that isless than a compressive stress in the fully open configuration andgreater than a compressive stress in the fully closed configuration.Various chemical strengthening embodiments are described below in moredetail with respect to FIGS. 9A-9C and 22-25.

The preformed geometry of the sheet component 602 of FIG. 6A maycorrespond to an intermediate configuration between the foldedconfiguration of FIG. 6B and the unfolded configuration of FIG. 6C. Asshown in FIG. 6A, the sheet component 602 is preformed to have bendportion 651 with a radius of curvature R₁ and bend angle θ₁. FIG. 6Bshows the sheet component 602 as folded in the closed configuration andhaving a bend region 652 with a radius of curvature R₂ and bend angle θ₂of 180 degrees. The bend regions adjoin regions 681 and 682. FIG. 6Cshows the sheet component 602 as unfolded in the open configuration andhaving an effective infinite radius of curvature R₃ and bend angle θ₃ of0 degrees. In this example, the bend angle θ₂ is greater than θ₁. Morespecifically, the bend angle θ₁ is approximately halfway between θ₂ andθ₃. If θ₃ is approximately 0 degrees and θ₂ is approximately 180degrees, then θ₁ may be approximately 90 degrees. In other embodiments,θ₁ may be biased closer to θ₂ or θ₃ depending on whether it is desirablefor the folded or the unfolded state, respectively, to have a loweroverall stress condition.

The shape and curvature of the sheet component 602 may also vary betweenthe preformed and folded configuration. In this example, R₂ is less thanR₁. However, in some implementations R₂ may be approximately equal toR₁. For example, the ratio of R₂/R₁ may vary from 0.25 to 1. In somecases, the ratio of R₂/R₁ may vary from 0.5 to 1. While the radius isdepicted as being a constant or single radius, the shape of the bend mayvary in accordance with some embodiments.

As mentioned previously, an annealing or heating operation may beperformed on the preformed sheet component to reduce or eliminatebending induced stress and/or residual stress. When a flat sheetcomponent is bent to the shape of FIG. 6A using, for example, a formingprocess above the glass transition temperature but below the softeningpoint, tensile and compressive stresses are induced in the sheetcomponent by the bending process. In particular, tensile stresses may beinduced on the outside of the bend and compressive stresses may beinduced on the inside of the bend. The annealing step of the preformingprocess at least partially relaxes these stresses induced by thepreforming bending operation. As another example, annealing reducesstresses acquired during cooling. In particular, by annealing afterbending into the preformed shape of FIG. 6B, the tensile stresses alongan outer region of the bend region are significantly reduced as comparedto a pre-annealed preformed sheet component. If the tensile andcompressive stresses are sufficiently reduced in the annealing process,the preliminary shape can have substantially no tensile or compressivestresses through the bend region.

After annealing, folding or bending the sheet component into either thefolded configuration of FIG. 6B or the unfolded configuration of FIG. 6Cwill induce compressive and/or tensile stress into the sheet component.Thus, the preformed configuration of FIG. 6A can correspond to a minimumstress condition for the sheet component. As mentioned previously, asurface compressive stress may be produced along the surface of thesheet component using a chemical strengthening process.

FIGS. 7A-7C depict a similar process as described above with respect toFIGS. 6A-6C with a different preformed geometry. FIG. 7B shows the sheetcomponent in a folded or closed configuration; the sheet component inthis shape has a bend region 752 with a radius of curvature R₁ and bendangle θ₂ of 180°. The bend region 752 adjoins regions 781 and 782. Asshown, bend angle θ₂ is greater than θ₁. FIG. 7C shows the sheetcomponent in an unfolded or open configuration, having an effectiveinfinite radius of curvature R₃. Similar to the previous example, thesheet component of FIG. 7A may be annealed after forming to reduce oreliminate stress through the bend region 752.

FIG. 7A depicts a side view of an example shape of a preformed sheetcomponent 702 having a radius of curvature equal to that of the covershape in the closed configuration. This preformed shape may result inless tensile stress in the closed configuration as compared to thepreformed shape of FIG. 6A. In some cases, the preformed shape of FIG.7A may bias the sheet component towards the folded or closedconfiguration of FIG. 7B. In FIG. 7A, the preformed sheet component hasbend portion 751 with a radius of curvature R₁ and bend angle θ₁. Thebending angle in FIG. 7A is smaller than that of FIG. 6A. The smallerbend angle of the preformed shape of FIG. 7A may also tend to reduce thestress in the folded or closed configuration of FIG. 7B and may alsobias the sheet component toward the folded configuration. Conversely,using the preformed shape of FIG. 7A, the stress may be increased forthe unfolded or open configuration of FIG. 7C, as compared to theunfolded or open configuration of FIG. 6C when using the preformed shapeof FIG. 7A.

As shown in FIGS. 6A and 7A, the bend portion of the preformed sheetcomponent has a substantially uniform radius of curvature. However, thebend portion of the preformed sheet component may also be formed toother shapes, as illustrated in FIGS. 8A, 8B and 8C. FIG. 8A illustratesa bend portion 851 of sheet 802 having a central flat region 821 withcurved corners 831, 841. FIG. 8B illustrates a bend portion 852 having acentral flat region 822 with curved corners 832, 842; the transitionbetween the central flat region and the corners is more gradual than inFIG. 8A. FIG. 8C illustrates a bend portion 853 with a smaller radius ofcurvature at the upper portion, including upper corner 833 and a largerradius of curvature at the lower portion, including lower corner 843.These shapes are provided by way of example and are not intended to belimiting in nature.

Several methods can be used to form the sheet component into thepreliminary or preformed shape and anneal it to reduce or eliminatebending induced stresses. In some embodiments, the forming process is ahot forming process in which the sheet component is heated to itssoftening point and then bent to the desired shape. In an example, thesheet component is cooled back down to ambient temperature at a slowenough rate so that no or virtually no residual stresses are left in thematerial.

As an example, a pair of plates is used to introduce a bend into thesheet as shown in FIGS. 9A-9C. The sheet component 902 may be generallyheated by a heat source 961 as shown in FIG. 9A or locally heated bysource 962 as shown in FIG. 9B. When the plates 971 and 972 are moved asindicated by the arrows, the preformed shape shown in FIG. 9C isobtained.

In another example, a mandrel is used to introduce a bend into the sheetcomponent. As shown in FIGS. 10A-10C, the sheet component 1002 issupported on plates 1075 and 1076 that are moved downwards during theforming process, allowing the sheet component to slump over the mandrel1073 or 1074. A variety of heat sources can be used, including a generalheat source 1061 or a local heat source 1062 as shown in FIGS. 10A-10Bor a heated mandrel 1074 as shown in FIG. 10C. FIG. 10D illustrates theshaped sheet component 1002 slumped or draped over the mandrel 1073. Ifdesired, the sheet component can be shaped to a tighter bend while thesheet component is draped over the mandrel 1073. For example, anotherpair of plates (not shown) can be used to move the non-bend portions ofthe sheet component towards each other.

In a further example, rollers are used to introduce a bend into thesheet component. As shown in FIG. 11A, the sheet component 1102 isplaced on a bed of rollers 1177 and generally heated with a heat source1161. The position of the rollers is then adjusted to bring the sheetcomponent to the desired shape as shown in FIG. 11B.

In some embodiments, at least a portion of the preformed sheet componentis strengthened to introduce a compressive stress layer in the sheetafter annealing. For example, the sheet component may be strengthened inits preformed or preliminary shape. When the preliminary shape isannealed to be essentially stress-free, such strengthening can producecompressive stresses on the outside of the bend in the preliminaryshape. The tensile stresses induced on the outside of the bend bybending the sheet component to the closed configuration are thus reducedby such strengthening. In embodiments, the compressive stresses due tochemical strengthening are greater than the tensile stresses induced bybending from the preliminary shape to the closed configuration. Inaddition, strengthening to produce compressive stresses on the inside ofthe bend in the preliminary shape can reduce the tensile stressesinduced on the inside of the bend by bending the sheet component to theopen configuration.

In another example, the cover glass in its preformed or preliminaryshape is adjusted to a tighter bend prior to strengthening to introducea compressive stress layer. Chemical strengthening can be enhanced onthe outside of the bend due to the tensile stresses induced by the shapeadjustment. FIG. 12A illustrates a preliminary shape of sheet component1202 as formed with bend 1251 of bend radius R₁, a bend angle θ₁ andannealed. FIG. 12B illustrates adjustment of the shape of FIG. 12A toform bend 1252 with a tighter bend angle θ₂ before strengthening. Insome instances, the bend radius R₂ may also be different than the bendradius R₁.

In general, chemically strengthening introduces a compressive stresslayer to improve the strength and impact resistance of the sheetcomponent 1202. By chemically strengthening the sheet component 1202 inan adjusted or further folded position as depicted in FIG. 12B, thecombined effect of chemical strengthening and bending can producecompressive stressing the outer portion of the bend region, furtherenhancing the impact resistance and strength of the sheet component 1202when in the folded or closed state. Furthermore, by chemicallystrengthening the sheet component 1202 in the adjusted or further foldedposition of FIG. 12B, the compressive stresses of the outer (or lower)portion of the sheet component 1202 in the unfolded or openconfiguration of FIG. 12C may also be further enhanced. However, whenthe inner portion of the foldable region is chemically strengthened to alesser extent that the outer portion, the reduction in the tensilestresses in the corresponding inner (or upper) portion of the sheetcomponent 1202 in the unfolded or open configuration may be reduced oreliminated. This may be an acceptable tradeoff if, for example, theinner (or upper) portion of the sheet component 1202 is facing inwardtoward the device and may be otherwise protected from impact.

In an alternative embodiment, the sheet component 1202 may be chemicallystrengthened when in the intermediate state or configuration of FIG.12A. In one example, the sheet component 1202 may be annealed to be in aminimum or reduced stress condition at the intermediate state orconfiguration of FIG. 12A. The sheet component 1202 may then bechemically strengthened while in this intermediate state orconfiguration.

FIG. 13 depicts an example cross-sectional view of a cover sheet 1302coupled to a display layer 1306 using cladding layer 1304. In someimplementations, a preforming process using a mandrel or other tool mayresult in a surface artifact in the cover sheet 1302 (e.g., a localizeddepression). The cladding layer 1304 can be used to fill the structuralartifact and camouflage or reduce the visual perceptibility of thesurface artifact in the final product. In addition, the cladding layer1304 can be used to fill other surface irregularities and may have anoptical index that is between an optical index of the cover sheet 1302and an optical index of a transparent substrate of the display layer1306.

As shown in FIG. 13, the cover sheet 1302 includes a depression orrecess that may be due to a localized thinning of the cover sheet 1302caused when heating and preforming the cover sheet 1302. The cover sheet1302 is positioned with the surface having the depression or recessfacing the display layer 1306. The cover layer 1302 also defines a flator uniform surface along an exterior surface of the device. As shown inFIG. 13, the cladding layer 1304 may fill the depression or recess,reducing or eliminating any visual impact. Attaching the cover sheet1302 with the depression or recess faced towards the display layer 1306may result in a smooth outer surface, which may enhance the appearanceof the device.

With regard to FIG. 13, the cladding layer 1304 may be formed from anoptically clear adhesive (OCA) or other type of bonding agent. In somecases, the cladding layer 1304 is formed from a glass material having amelting temperature that is lower than the melting temperature of thecover sheet 1302 and the display layer 1306. The cladding layer 1304,when melted or otherwise in a flowing state, fills the surface artifactwhile also forming a bond between the cover sheet 1302 and the displaylayer 1306.

In some implementations, features are formed into the substrate or glassof the cover sheet to facilitate bending at a particular location. Thefeatures may reduce the internal stress in the substrate or glass andmay also help the cover sheet bend in a predictable and repeatablemanner. The features may include an array of cuts or reliefs having ashape that is configured to facilitate a particular bend or livinghinge. The cuts or reliefs that are formed into the cover sheet may befilled with a more flexible or pliable material that is optically indexmatched to the substrate or glass of the cover sheet. When the featureincludes an array of relief features, each filler may be one of a set offillers, each filler of the set of fillers being disposed in a relieffeature of the array. In some embodiments, a relief feature may becharacterized by one or more dimensions such as a width or a depth.

FIGS. 14A-19B depict different example embodiments of relief featuresformed into a substrate and filled with a flexible or pliable material.With respect to the following examples, a cover sheet may be formed froma translucent or transparent ceramic substrate and define one or morerelief features. The relief features of the substrate may be partiallyor completely filled with a filler or filler material. The substrate maybe formed from a glass sheet or other type of translucent or transparentceramic material. While this is provided as merely an example, thesubstrate may be formed from other optically translucent materialsincluding, for example, sapphire, polymer, and/or laminated layers ofmultiple sheets.

FIGS. 14A-14B depict two example cover sheets having relief features. InFIG. 14A, the cover sheet 1400 a includes a substrate 1402 a having asingle relief feature 1404 a formed into a surface 1412 a of thesubstrate 1402 a. The relief feature 1404 a reduces the thickness of thesubstrate 1402 a over a bend region 1410 a. The relief feature 1404 amay also be referred to as a localized thinning of the substrate 1402 aand serves to reduce the internal stress experienced by the substrate1402 a when the cover sheet 1400 a is folded between flat and bentstates. A relief feature generally includes a wall and may include apair of opposing walls. As example, a wall can be substantiallyperpendicular to a surface or form an oblique angle with respect to thesurface. FIG. 14A illustrates wall 1408 a substantially perpendicular tosurface 1412 a.

As shown in FIG. 14A, the relief feature 1404 a is filled with filler1406 a. The filler 1406 a may include a flexible, pliable, or otherwisenon-rigid material that is able to deform as the cover sheet 1400 a isfolded along the bend region 1410 a. In some implementations, the filler1406 a is a polymer, which may have an optical index substantiallymatched to the substrate 1402 a. Polymers capable of adhering to thesubstrate include, but are not limited to, acrylic-based polymers andsilicone-based polymers. As an example, the polymer is an opticallyclear adhesive.

FIG. 14B depicts another example cover sheet 1400 b having multiplerelief features 1404 b formed into a surface to define a bend region1410 b. FIG. 14B illustrates wall 1408 b forming an oblique angle withrespect to surface 1412 b. Similar to the example provided above withrespect to FIG. 14A, the relief features 1404 b are each filled with afiller 1406 b. Also similar to the previous example, the filler 1406 bmay include a flexible, pliable, or otherwise non-rigid material that isoptically index matched to the substrate 1402 b. The relief features1404 b create multiple thinned portions, which may reduce the stressexperienced by the substrate 1402 b when bending.

One potential advantage to the configuration of FIG. 14B is that themultiple or array of relief features 1404 b may result in a moreconsistent or uniform bend radius throughout the bend region 1410 b whenthe cover sheet 1400 b is folded. The array of relief features 1404 bmay also provide a more flat or uniform thickness when the cover sheet1400 b is flat or unfolded. As described in more detail below withrespect to FIGS. 18A-20B, the size and shape of the relief features 1404b may vary to produce different bend configurations or bend shapes whenthe cover sheet 1400 b is folded.

FIG. 14C illustrates a folded configuration of an electronic device 1401c including a cover sheet 1400 c similar to that of FIG. 14A. As shownin FIG. 14C, the cover sheet 1400 c includes a substrate that may beformed from a ceramic material that defines an exterior surface of theelectronic device over the bend or foldable region 1410 c. By using aceramic material along the foldable region 1410 c, the device 1401 c mayhave improved strength or durability when in the folded configuration.As shown, the display layer 1416 c is sufficiently flexible to generallyconform to the shape of the cover sheet in the folded configuration.Example flexible display layers are discussed in more detail withrespect to FIG. 26. As shown in FIG. 14C, the device 1401 c includes acover sheet 1400 c, optional adhesive 1414 c, display layer 1416 c, andbacking layer 1418 c. The foldable region 1410 c, relief feature 1404 c,and filler 1406 c of the cover sheet are also shown. The adhesive 1414 ccouples or attaches the cover sheet 1400 c to the display layer 1416 c.The adhesive 1414 c is shown as a continuous layer, but in other exampleconfigurations the adhesive may not form a continuous layer or may beabsent. The backing layer 1418 c is depicted as a single component inFIG. 14C for simplicity. However, the backing layer 1418 c may includeone or more other components of the electronic device 1401 c, asdescribed in more detail below with respect to FIG. 26. One or more ofthe components may be flexible or bendable and extend across thefoldable region 1410 c. The backing layer 1418 c or other devicecomponents may be attached to the display layer 1416 c with an adhesivein a similar manner as described for adhesive 1414 c.

FIGS. 15A-15B depict example cover sheets having an array of relieffeatures formed on each of two sides of a substrate. In particular, asshown in FIG. 15A, the cover sheet 1500 a includes a substrate 1502 ahaving a first array of relief features 1504 a formed along a firstsurface and a second array of relief features 1506 a formed along asecond surface opposite to the first surface. Similar to the previousexamples, the relief features 1504 a and 1506 a are filled with a filler1508 a. Similar to the previous examples, the filler 1508 a may beformed from a flexible, pliable, or otherwise non-rigid materialincluding but not limited to optically clear adhesives or polymermaterials.

The cover sheet 1500 a of FIG. 15A may provide several advantages.Specifically, the relief features 1504 a and 1506 a form a series oflocally thinned regions. Similar to the previous examples, the locallythinned region may reduce the overall stress in the substrate 1502 awhen being folded or bent. Additionally, having relief features 1504 aand 1506 a formed on opposite sides of the substrate 1502 a, the locallythinned portions of the substrate 1502 a are located closer to theneutral axis of the cover sheet 1500 a. Thus, the stress produced withinthe locally thinned regions may be further reduced or minimized. Byhaving relief features 1504 a and 1506 a formed on opposite sides of thesubstrate 1502 a, the cover sheet 1500 a may be able to bend around asmaller radius without exceeding a threshold or safe stress level withinthe substrate 1502 a.

FIG. 15B depicts another example cover sheet 1500 b. Similar to theprevious example, the substrate 1502 b includes a first array of relieffeatures 1504 b formed on a first surface and a second array of relieffeatures 1506 b formed on a second, opposite side. Both arrays of relieffeatures 1504 b and 1506 b are filled with a filler 1508 b, similar toas described above with respect to FIG. 15A. In addition, the coversheet 1500 b also includes an outer cover layer 1510 b positioned overthe side of the substrate 1502 b having the first array of relieffeatures 1504 b. The outer cover layer 1510 b may be formed form aceramic material and may define a smooth continuous surface along thefoldable region of the device.

The outer cover layer 1510 b may provide a uniform outer surface for thecover sheet 1500 b. A more uniform or continuous outer surface mayenhance the visual appearance of the cover sheet 1500 b as well asproviding a more uniform feel to the touch. In some cases, the outercover layer 1510 b provides enhanced scratch resistance for the coversheet 1500 b. The outer cover layer 1510 b may be formed from chemicallystrengthened glass, sapphire, or other scratch-resistant material.

As shown in FIG. 15B, the outer cover layer 1510 b may be attached orcoupled to the substrate 1502 b by an adhesive layer 1512 b. In someimplementations, the interface between the outer cover layer 1510 b andthe rest of the cover sheet 1500 b may be configured to reduce thestress produced in the outer cover layer 1510 b when the cover sheet1500 b is folded. For example, the adhesive layer 1512 b may beconfigured to provide some compliance in shear to allow the outer coverlayer 1510 b to shift or slip with respect to the substrate 1502 b whenthe cover sheet 1500 b is folded and/or unfolded. The shear compliancemay allow the outer cover layer 1510 b to bend about a neutral axis thatis located within or near the outer cover layer 1510 b thereby reducingthe stress produced in the outer cover layer 1510 b. Alternatively, theadhesive layer 1512 b may have a high resistance to shear and stronglycouple the outer cover layer 1510 b to the substrate 1502 b. This maymove the neutral axis of the outer cover layer 1510 b to a region withinthe substrate 1502 b, which may stiffen or strengthen the cover sheet1500 b.

FIG. 16 depicts an example cover sheet having two asymmetrical sets ofrelief features formed in opposite sides. Specifically, the cover sheet1600 includes a first set of relief features 1604 formed on a firstsurface and each of the relief features in the first set having a widththat is narrower as compared to each of the relief features in a secondset of relief features 1606 formed on a second, opposite surface of thesubstrate 1602. Similar to the previous examples, the cover sheet 1600includes a filler 1608, which may be formed from a flexible, pliable, orotherwise non-rigid material including but not limited to opticallyclear adhesives or polymer materials.

This configuration may provide a more consistent or uniform outersurface due to the narrower relief features 1604. In some cases, thenarrower relief features 1604 are visually and/or tacticallyimperceptible when the cover sheet 1600 is in a flat or unfoldedconfiguration. In some cases, the asymmetric nature of the relieffeatures enhances the flexibility for the cover sheet 1600 in a givenbend direction. For example, the wider relief features 1606 formed onthe second surface of the substrate 1602 may enhance the flexibility ofthe cover sheet 1600 when bent inwardly along the second surface.

FIGS. 17A and 17B depict an unfolded and folded state of an examplecover sheet having relief features that limit the bend radius of thecover sheet when the side having the relief features is on the inside ofthe bend. As shown in FIGS. 17A and 17B, the relief features areprovided on one side or surface of the sheet. In other embodiments, suchas when the cover sheet forms an S-shaped bend, relief features may beprovided on both sides or opposing surfaces of the sheet. In general,the size and shape of the relief features may control the minimum bendradius of the cover sheet. As shown in FIGS. 17A and 17B, the coversheet 1700 includes a substrate 1702 having relief features 1704 formedinto a surface and filled with filler 1708. The filler 1708 may be anon-rigid material, similar to as described above with respect to otherexamples.

As shown in FIG. 17B, the minimum bend radius 1710 may be determined bythe size and shape of the relief features 1704. Specifically, as thecover sheet 1700 is folded, the relief features 1704 begin to collapseand compress the filler 1708. The minimum bend radius 1710 may bedetermined by the amount of bending at which the filler 1708 reaches amaximum compression. In some cases, the minimum bend radius 1710corresponds to the amount of bending in which the relief features 1704can no longer collapse further. In general, the wider or larger therelief features 1704, the smaller or tighter the minimum bend radius1710. Conversely, the narrower or smaller the relief features 1704, thelarger the minimum bend radius 1710. A tapered or angled shape of therelief feature 1704, as shown in FIGS. 17A and 17B, may also determinethe minimum bend radius 1710.

FIGS. 18A and 18B depict an unfolded and folded state of an examplecover sheet having relief features that form a generally flattened edgealong a bend in the cover sheet. As shown in FIGS. 18A and 18B, therelief features are provided on one side of the sheet. In otherembodiments, such as when the cover sheet forms an S-shaped bend, relieffeatures may be provided on both sides of the sheet. In general, relieffeatures may be grouped or arranged along a surface of the substrate toprovide a desired geometry, such as a flat or straight region within thebend. As shown in FIGS. 18A and 18B, the cover sheet 1800 includes asubstrate 1802 having a first set of relief features 1804 and a secondset of relief features 1806 formed into a surface and filled with filler1808. The filler 1808 may be a non-rigid material, similar to asdescribed above with respect to other examples.

As shown in FIGS. 18A and 18B, the first and second sets of relieffeatures 1804 and 1806 result in two localized bends, each having a bendradius 1810. The two bends are separated by a flat region 1812, whichmay have a substantially flat or straight geometry. In this example, theflat region 1812 does not include any relief features, which may helpmaintain the flatness or straightness of the flat region 1812 as thecover sheet 1800 is folded. In some cases, the flat region 1812 includesa small amount of bowing and is not perfectly flat.

FIGS. 19A and 19B depict an unfolded and folded state of an examplecover sheet having relief features that form an arced or bowed edgealong a bend in the cover sheet. As shown in FIGS. 19A and 19B, therelief features are provided on one side of the sheet. In otherembodiments, such as when the cover sheet forms an S-shaped bend, relieffeatures may be provided on both sides of the sheet. In general, sets ofdifferently sized relief features may be grouped or arranged along asurface of the substrate to provide a desired geometry, such as an arcedor bowed region within the bend. As shown in FIGS. 19A and 19B, thecover sheet 1900 includes a substrate 1902 having a first set of relieffeatures 1904, a second set of relief features 1905, and a third set ofrelief features 1906 formed between the first and second sets. Therelief features may be filled with a filler 1908, which may be anon-rigid material, similar to as described above with respect to otherexamples.

As shown in FIGS. 19A and 19B, the first and second sets of relieffeatures 1904 and 1906 result in two localized bends, each having a bendradius 1910. The two bends are separated by a bowed region 1912, whichhas an arc radius 1914 that is substantially larger than the bend radii1910. In this example, the shape of the bowed region 1912 is due, inpart, to the size and shape of the third set of relief features 1906. Ingeneral, the third set of relief features 1906 are smaller or narrowerthan the first and second sets of relief features 1904 and 1905 when thecover sheet is unfolded, which results in the larger arc radius 1914.FIGS. 19A and 19B are provided as an example, and the relief geometry,relief spacing, or other aspects of the relief arrangement may be variedto produce a similar result.

For each of the examples described above with respect to FIGS. 14A-19B,the relief cuts may be formed into the surface of the substrate usingvarious machining operations or techniques. For example, the relief cutsmay be formed using a laser ablation, chemical etching, grinding, orother similar material removal technique. Also, for each of the examplesdescribed above with respect to FIGS. 14A-19B, the respective bendregions may be preformed in accordance with the preforming embodimentsdescribed above with respect to FIGS. 6A-12B.

FIGS. 20A-20B depict example cover sheets formed from a laminated stackof layers. The laminated stack of layers may define one or more relieffeatures or locally thinned regions that facilitate bending or foldingthe cover glass. In particular, FIG. 20A depicts cover sheet 2000 ahaving a laminated stack of layers including an outer layer 2002 abonded to inner layers 2004 a and 2006 a by an interface layer 2012 a.As shown in FIG. 20A, a recess or relief feature is formed between thelayers and filled with filler 2008 a. The relief features may be filledwith filler 2008 a, which may be a pliable or non-rigid material,similar to as described above with respect to other examples.

FIG. 20B depicts another configuration of a cover sheet 2000 b having anouter layer 2002 b bonded to multiple inner layers 2004 b, 2005 b, and2006 b by an interface layer 2012 b. As shown in FIG. 20B, the multipleinner layers 2004 b, 2005 b, and 2006 b define multiple recesses orrelief features between each inner layer. Similar to as described above,the relief features may be filled with a filler 2008 b, which may be apliable or non-rigid material.

The laminated cover sheets 2000 a and 2000 b of FIGS. 20A and 20B havingrelief features may facilitate bending or folding in a manner similar toas described above with respect to FIGS. 14A-19B. In particular, havingone or more locally thinned regions formed into the cover sheet mayreduce the amount of stress produced within one or more of thesubstrates while the cover sheet is folded and/or unfolded. Similar tothe previous examples, the recesses can be formed on opposing sides ofthe cover sheet and may vary in size and shape to provide a particularbend geometry or shape.

The laminated cover sheets 2000 a and 2000 b of FIGS. 20A and 20B mayprovide manufacturing advantages over other techniques. For example, thelaminated cover sheets 2000 a and 2000 b may be formed using a glasslamination process that does not require a material removal operation toform the relief features. This may save time and simplify themanufacturing process. It may also provide some ability to rework and/orcorrect manufacturing defects because the relief features are notpermanently formed into a particular article.

The laminated technique depicted in FIGS. 20A and 20B also allowsdifferent materials to be used to enhance the performance of the coversheets 2000 a and 2000 b. For example, the outer layers 2002 a and 2002b may be formed from a hard or scratch-resistant material, such assapphire or strengthened glass. The inner layers 2004 a, 2006 a, 2004 b,2005 b, and 2006 b may be formed from a material having lower hardnessor greater pliability as compared to the outer layers 2002 a and 2002 b.Accordingly, the material properties of each layer may be selected for aparticular purpose to provide an enhanced composite cover sheet.

In some implementations, the interface layers 2012 a and 2012 b may beconfigured to provide a particular flexibility and/or stress profilewithin the cover sheets 2000 a and 2000 b. For example, an interfacelayer 2012 a, 2012 b having a high resistance to shear may produce astiffer or more rigid cover sheet 2000 a, 2000 b. By not allowing theouter layer to slip or shift with respect to the inner layers, the coversheet may have a higher overall bending moment, which enhances thestrength and rigidity of the cover sheet. In some embodiments, the outerlayers 2002 a and 2002 b are fused (without adhesive) to correspondinginner layers 2004 a, 2006 a, 2004 b, 2005 b, 2006 b to form a joint thatis highly resistant to shear. An interface layer 2012 a, 2012 b having alow resistance to shear may be used in order to allow relative slipbetween the layers and lower the overall stress in each of the layers.This may be helpful in configurations in which the outer layer is verythin and/or may have a reduced ability to withstand high internalstress.

When the outer layers and inner layers have a different index ofrefraction, the interface layers 2012 a, 2012 b may provide transitionin index of refraction between the outer and inner layers to improve thetransmissivity of the stack. For example, when the inner and outerlayers have a different optical index of refraction, the interface mayprovide a transition in optical index of refraction. This may alsoreduce reflection or other visual artifacts created by the bond betweenouter and inner layers. In some instances, the interface layers 2012 a,2012 b are doped or treated to produce an index gradient through thethickness of the interface layers 2012 a, 2012 b. For example, theinterface layers 2012 a, 2012 b may be treated to have an index thatgradually increases (or gradually decreases) across the depth of theinterface layers 2012 a, 2012 b to match the corresponding opticalindexes of the inner and outer layers. In one example implementation,the interface layers 2012 a, 2012 b include an aluminum particulate thatis sputtered into a glass or other matrix. The concentration of thealuminum particulate may vary with the depth, thereby varying theoptical index of the interface layers 2012 a, 2012 b.

FIG. 20C illustrates a folded configuration of an electronic deviceincluding a cover sheet 2000 c similar to that of FIG. 20A. As shown inFIG. 20C, the cover sheet 2000 c includes a substrate that may be formedfrom a ceramic material that defines an exterior surface of theelectronic device over the bend or foldable region 2010 c. By using aceramic material along the foldable region 2010 c, the device 2001 c mayhave improved strength or durability when in the folded configuration.As shown, the display layer 2016 c is sufficiently flexible to generallyconform to the shape of the cover sheet in the folded configuration.Example flexible display layers are discussed in more detail withrespect to FIG. 26. As shown in FIG. 20C, the device 2001 c includes acover sheet 2000 c, optional adhesive 2014 c, display layer 2016 c, andbacking layer 2018 c. The bend region 2010 c, outer layer 2002 c, innerlayers 2004 c, 2006 c, filler 2008 c, and interface layer 2012 c of thecover sheet are also shown. The adhesive 2014 c couples or attaches thecover sheet 2000 c to the display layer 2016 c. The adhesive 2014 c isshown as a continuous layer, but in other example configurations theadhesive may not form a continuous layer or may be absent. The backinglayer 2018 c is depicted as a single component in FIG. 20C forsimplicity. However, the backing layer 2018 c may include one or morecomponents of the electronic device 2001 c, as described in more detailbelow with respect to FIG. 26. One or more of the components may beflexible or bendable and extend across the foldable region 2010 c. Thebacking layer 2018 c or other device components may be attached to thedisplay layer 2016 c with an adhesive in a similar manner as describedfor adhesive 2014 c.

FIGS. 21A and 21B depict example cover sheets having multiple panelsintegrated with a flexible substrate. The multiple panels or sectionsmay also facilitate bending or folding of the cover sheet. As shown inFIG. 21A, the cover sheet 2100 a includes multiple panel layers orpanels 2102 a coupled to a base layer or substrate 2104 a. In someimplementations, each panel 2102 a is formed from a relatively hardrigid material and the substrate 2104 a is formed from a more pliableflexible material. In one example, each of the panels 2102 a is formedfrom a glass or sapphire sheet and the substrate 2104 a is formed from apolymer sheet. In some embodiments, the panels 2102 a form the outersurface of the cover sheet 2100 a. In some cases, the panels 2102 a arecovered on both sides with a protective layer or substrate.

As shown in FIG. 21A, the panels 2102 a are arranged with small gaps orspaces between the panels to define locally thinned regions of the coversheet 2100 a. In some instances, the gaps or spaces may be filled with afiller, similar to as described above with respect to other embodiments.The locally thinned regions may allow the cover sheet 2100 a to bend orfold in a manner similar to other examples provided above with respectto FIGS. 14A-20B. Also similar to the previous examples, the size,shape, and spacing of the various gaps may determine or facilitate aparticular bend or fold.

FIG. 21B depicts a cover sheet 2100 b having multiple panel layers orpanels 2102 b that are pressed, embedded, or formed into the base layeror substrate 2104 b. In this example, the panels 2102 b are at leastpartially embedded into a surface of the substrate 2104 b and thesubstrate 2104 b is able to deform sufficiently to fill the gaps betweenthe panels 2102 b, eliminating the need for a filler or other materialto occupy the space between the panels 2102 b. Similar to the previousexample, the gaps between the panels 2102 b facilitate bending of thecover sheet 2100 b and may be arranged or configured to produce aparticular bend geometry or shape. Also similar to the previous example,the panels 2102 b may be formed from a hard sheet, such as strengthenedglass or sapphire and the substrate 2104 b may be formed from a polymer.

FIG. 21C illustrates a folded configuration of an electronic deviceincluding a cover sheet 2100 c similar to that of FIG. 21A. As shown inFIG. 21C, the cover sheet 2100 c includes a substrate that may be formedfrom a ceramic material that defines an exterior surface of theelectronic device over the bend or foldable region 2110 c. By using aceramic material along the foldable region 2110 c, the device 2101 c mayhave improved strength or durability when in the folded configuration.As shown, the display layer 2116 c is sufficiently flexible to generallyconform to the shape of the cover sheet in the folded configuration.Example flexible display layers are discussed in more detail withrespect to FIG. 26. As shown in FIG. 21C, the device 2101 c includes acover sheet 2100 c, optional adhesive 2114 c, display layer 2116 c, andbacking layer 2118 c. The bend region 2110 c, panels 2102 c, andsubstrate 2104 c of the cover sheet are also shown. The adhesive 2114 ccouples or attaches the cover sheet 2100 c to the display layer 2116 c.The adhesive 2114 c is shown as a continuous layer, but in other exampleconfigurations the adhesive may not form a continuous layer or may beabsent. The backing layer 2118 c is depicted as a single component inFIG. 21C for simplicity. However, the backing layer 2118 c may includeone or more components of the electronic device 2101 c, as described inmore detail below with respect to FIG. 26. One or more of the componentsmay be flexible or bendable and extend across the foldable region 2110c. The backing layer 2118 c or other device components may be attachedto the display layer 2116 c with an adhesive in a similar manner asdescribed for adhesive 2114 c.

In some embodiments, ceramic cover sheet layers or substrates asdescribed herein are strengthened before being placed into theelectronic device. In an example, an inorganic glass sheet component ischemically strengthened by an ion exchange process which inducescompressive stress in a surface layer of the sheet component.Alternately, a field-assisted chemical strengthening process or an ionbombardment process is used to introduce ions into the cover sheet,thereby inducing compressive stress in the sheet component. The depth ofthe compressive stress layer and the peak compressive stress can be usedas measures of the amount of strengthening. In some embodiments the peakcompressive stress is at the surface of the cover glass while in othercomponents the peak compressive stress may be located below the surfaceof the cover glass. The un-strengthened central portion of the sheetcomponent typically experiences tensile stress when a compressive stresslayer is formed; the central tension of the sheet can be used as ameasure of the tensile stress.

Glass compositions suitable for ion exchange or field assisted chemicalstrengthening include, but are not limited to, alumina silicate glass(aluminosilicate glass), soda lime glass, borosilicate glass or lithiumcontaining glass. For an ion exchange process conducted primarily attemperatures below the strain point of the glass, ions in the glass areexchanged with larger ions to set up compressive stresses in an outerlayer of the glass. For example, the ion exchange process may involvethe exchange of alkali metal ions, such as the exchange of sodium ionsfor potassium ions or the exchange of lithium ions for sodium ions. Inan example, the chemical strengthening process involves exposing theglass to a medium containing the larger ion, such as by immersing theglass in a bath containing the larger ion or by spraying or coating theglass with a source of the ions. For example, a salt bath comprising theion of interest (e.g., a potassium nitrate bath) may be used for ionexchange. Suitable temperatures for ion exchange are above roomtemperature and are selected depending on process requirements. Inembodiments, the chemical strengthening process includes one or more ionexchange steps. A multi-step ion exchange chemical strengthening processmay comprise a step of exchanging ions in the glass for larger ions,followed by a step of exchanging some of the larger ions introduced inthe previous step for smaller ions.

Selective chemical strengthening of a sheet component can be achievedthrough masking techniques. For example, portions of the sheet componentwhich are to be strengthened to a lesser depth are masked before thesheet component is exposed to the ion exchange medium. After chemicalstrengthening of the rest of the sheet component, the mask can beremoved. If desired, additional chemical strengthening steps can be usedto obtain the desired levels of chemical strengthening. Additionalmasking steps can also be used to obtain the desired chemicalstrengthening profile. Suitable masking materials include, but are notlimited to, metals, polymers, and ceramics. In some embodiments,photolithographic patterning or etching are used to pattern the maskmaterial.

In some embodiments, a sheet component is selectively strengthened sothat some portions of the sheet component are strengthened to a greaterextent than others. For example, thinner portions of sheet componentscan be strengthened to a shallower depth than thicker portions. FIG. 22illustrates a cross-sectional view of a sheet component 2202 with arelief feature 2204 which has been chemically strengthened. As describedwith respect to the embodiments of FIGS. 14A-20C above, the relieffeature may create a localized thinning of the sheet component andfacilitate bending or folding of the sheet component. The depth D1 ofthe chemically strengthened layer in the locally thinned portion is lessthan the depth D2 in the adjoining portions. The smaller depth of layerin the locally thinner portion can limit the tension in the centralportions of the locally thinned portion. For the purposes of comparison,the layer depth D1 is also shown in the other portion of sheet component2202. FIG. 23 illustrates masking of the locally thinned portions 2304of a sheet component 2302 with mask 2306. After chemical strengtheningof the rest of the sheet component, the mask 2306 can be removed and thewhole sheet component then chemically strengthened. Such a process canprovide the chemical strengthening depth profiles of FIG. 22. Thelocation of the chemically strengthened layer is indicated with dotpatterns in FIG. 22; the higher density of the dot pattern near thesurfaces of the sheet component schematically illustrates a higherconcentration of ions introduced through ion exchange near the surfaces.

Another example of selective strengthening is illustrated by FIG. 24A,which shows a shallower compressive stress layer D1 on the bottom ofsheet component 2400 and a deeper compressive layer D2 on the top ofsheet component 2400. As in FIG. 22, the location of the chemicallystrengthened layer is indicated with a dot pattern in FIG. 24A. FIG. 24Bschematically illustrates the asymmetric compressive stress levels alongthe thickness of the sheet component. The chemical strengthening depthprofile illustrated in FIG. 24A can also be obtained using a maskingtechnique.

FIG. 25 is a flowchart providing an example process 2500 for producing aflexible bendable sheet component. In accordance with the embodimentsdescribed herein, the sheet component may be used to form a cover layerfor an electronic device. In particular, the process 2500 may be used toform a pre-shaped sheet component. When the pre-shaped sheet componentis used in an electronic device, a reduced stress condition may beproduced when the electronic device is in the fully folded or fullyunfolded configuration. In some embodiments, at least a portion of thepre-shaped sheet component has a reduced stress condition or a minimumstress condition when in an intermediate configuration (as compared to afully folded or fully unfolded configuration). In addition, the reducedstress condition can be assessed by comparing the magnitude of thestress at an inner portion and/or an outer portion of the foldableregion in the intermediate preformed configuration to the magnitude ofthe stress at the corresponding inner portion and/or outer portion ofthe foldable region in the fully folded and/or fully unfoldedconfiguration. For example, when the outer portion of the foldableregion has a compressive stress in the unfolded configuration and atensile stress in the folded configuration, the magnitude of the stressin the outer portion in the intermediate configuration may be less thanthe magnitude of the stresses in this portion in either the unfolded orfolded configuration.

In operation 2502, the sheet component is bent into a preformed orpreliminary shape or configuration. In some cases, the sheet componentmay be heated to increase the pliability or flexibility of the partwhile forming. Example techniques for bending the sheet component areprovided above in, for example, FIGS. 9A-11B. In some instances, theoperation 2502 is performed on a substrate, such as a glass sheet. Theglass sheet may include one or more relief features, as described abovewith respect to FIGS. 14A-20C.

The temperature of a ceramic sheet component may be elevated tofacilitate bending. For inorganic glasses, plots of viscosity versustemperature can be used to identify points relevant to deformation ofthe glass. For example, the strain point (viscosity of about 10^(14.5)Poise) is the temperature at which internal stress in the glass isrelieved in hours. The annealing point (viscosity of about 10^(13.4)Poise) is the temperature at which internal stress in the glass isrelieved in minutes. The glass transition temperature (viscosity ofabout 10¹³ Poise) is the temperature at which glass transitions fromsuper-cooled liquid to glassy state. The softening point is defined by aviscosity of about 10^(7.6) Poise while the working point is defined bya viscosity of about 10⁴ Poise. For crystalline ceramics, an annealingtemperature range may be defined at which substantial stress relaxationoccurs. An example temperature range for alumina may be fromapproximately 1700° C. to approximately 1950° C.

In embodiments, a glass sheet is heated to a temperature above thestrain temperature, at or above an annealing temperature, or at or abovea glass transition temperature. In further embodiments, the glass sheetis heated to a temperature at or below the working temperature, at orbelow a softening temperature, or at or below an annealing temperature.These ranges may be combined, so that, for example, the glass sheet maybe heated at or above an annealing temperature and at or below asoftening temperature. In other embodiments, a ceramic sheet other thana glass sheet is heated to a temperature at or above an annealingtemperature and less than a melting temperature.

In operation 2504, the sheet component may be annealed. In particular,the sheet component may be heated above a threshold temperature and heldabove that temperature allowing the glass to flow and reduce theresidual stresses within the foldable or bend region. As statedpreviously, the residual stresses may be reduced or eliminated,depending on the extent of the annealing operation. In some instances,the bending operation of 2502 and the annealing operation of 2504 canoverlap, as in a hot forming process.

In operation 2506, the sheet component may be further bent or folded inpreparation for the chemical strengthening of operation 2508. Forexample, the sheet component may be further unfolded to have a greaterbend angle or further folded to have a lesser bend angle and held whileperforming the chemical strengthening operation of 2508. This is anoptional operation that corresponds to the technique discussed abovewith respect to FIGS. 12A-12C.

In operation 2508, the sheet component may be chemically strengthened.As discussed previously, the chemical strengthening can be performedwhile the sheet component is in the preformed shape or in a furtherfolded (or further unfolded) shape in accordance with operation 2506,above. The chemical strengthening of operation 2508 may produce asubstantially uniform compressive stress in the sheet component.Alternatively, the chemical strengthening may produce an asymmetric orvarying compressive stress layer(s) in accordance with the techniquesdescribed above with respect to FIGS. 22-24B.

After the last step in the process, the pre-shaped sheet componentdefines a foldable region. In embodiments, the foldable region includesat least a portion of a bend region of the preliminary or preformedshape of the sheet component. In further embodiments, a preliminaryshape of the sheet component includes at least two bend regions so thatat least two foldable regions are produced in the pre-shaped sheetcomponent.

FIG. 26 is a block diagram of example components of an exampleelectronic device that may include a bendable or flexible layer asdescribed herein. The schematic representation depicted in FIG. 26 maycorrespond to components of the devices depicted in FIGS. 1-26,described above. However, FIG. 26 may also more generally representother types of electronic devices with a bendable or flexible layerincorporating a foldable region. Internal components of the electronicdevice may extend across the foldable region and may be flexiblethemselves. For example, electronic devices with a bendable or flexiblecover layer may include other flexible components such as a flexibledisplay, a flexible circuit board, a flexible battery, and combinationsthereof.

In embodiments, an electronic device with a bendable cover region andflexible display may also include sensors 2620 to provide informationregarding configuration and/or orientation of the electronic device inorder to control the output of the display. For example, a portion ofthe display 2614 may be turned off, disabled, or put in a low energystate when a folded or partially folded configuration of the device 2600results in all or part of the viewable area of the display 2614 beingblocked or substantially obscured. As another example, the display 2614may be adapted to rotate the display of graphical output based onchanges in orientation of the device 2600 (e.g., 90 degrees or 180degrees) in response to the device 2600 being rotated. As anotherexample, the display 2614 may be adapted to rotate the display ofgraphical output in response to the device 2600 being folded orpartially folded, which may result in a change in the aspect ratio or apreferred viewing angle of the viewable area of the display 2614.

The electronic device 2600 also includes a processor 2604 operablyconnected with a computer-readable memory 2602. The processor 2604 maybe operatively connected to the memory 2602 component via an electronicbus or bridge. The processor 2604 may be implemented as one or morecomputer processors or microcontrollers configured to perform operationsin response to computer-readable instructions. The processor 2604 mayinclude a central processing unit (CPU) of the device 2600. Additionallyand/or alternatively, the processor 2604 may include other electroniccircuitry within the device 2600 including application specificintegrated chips (ASIC) and other microcontroller devices. The processor2604 may be configured to perform functionality described in theexamples above. In addition, the processor or other electronic circuitrywithin the device may be provided on or coupled to a flexible circuitboard in order to accommodate folding or bending of the electronicdevice. A flexible circuit board may be a laminate including a flexiblebase material and a flexible conductor. Example base materials forflexible circuit boards include, but are not limited to, polymermaterials such as vinyl (e.g., polypropylene), polyester (e.g.,polyethylene terephthalate (PET), biaxially-oriented PET, andpolyethylene napthalate (PEN)), polyimide, polyetherimide,polyaryletherketone (e.g., polyether ether ketone (PEEK)), fluoropolymerand copolymers thereof. A metal foil may be used to provide theconductive element of the flexible circuit board.

The memory 2602 may include a variety of types of non-transitorycomputer-readable storage media, including, for example, read accessmemory (RAM), read-only memory (ROM), erasable programmable memory(e.g., EPROM and EEPROM), or flash memory. The memory 2602 is configuredto store computer-readable instructions, sensor values, and otherpersistent software elements

The electronic device 2600 may include control circuitry 2606. Thecontrol circuitry 2606 may be implemented in a single control unit andnot necessarily as distinct electrical circuit elements. As used herein,“control unit” will be used synonymously with “control circuitry.” Thecontrol circuitry 2606 may receive signals from the processor 2604 orfrom other elements of the electronic device 2600.

As shown in FIG. 26, the electronic device 2600 includes a battery 2608that is configured to provide electrical power to the components of theelectronic device 2600. The battery 2608 may include one or more powerstorage cells that are linked together to provide an internal supply ofelectrical power. The battery 2608 may be operatively coupled to powermanagement circuitry that is configured to provide appropriate voltageand power levels for individual components or groups of componentswithin the electronic device 2600. The battery 2608, via powermanagement circuitry, may be configured to receive power from anexternal source, such as an alternating current power outlet. Thebattery 2608 may store received power so that the electronic device 2600may operate without connection to an external power source for anextended period of time, which may range from several hours to severaldays. The battery may be flexible to accommodate bending or flexing ofthe electronic device. For example, the battery may be mounted to aflexible housing or may be mounted to a flexible printed circuit. Insome cases, the battery is formed from flexible anodes and flexiblecathode layers and the battery cell is itself flexible. In some cases,individual battery cells are not flexible, but are attached to aflexible substrate or carrier that allows an array of battery cells tobend or fold around a foldable region of the device.

In some embodiments, the electronic device 2600 includes one or moreinput devices 2610. The input device 2610 is a device that is configuredto receive input from a user or the environment. The input device 2610may include, for example, a push button, a touch-activated button, atouch screen (e.g., a touch-sensitive display or a force-sensitivedisplay), capacitive touch button, dial, crown, or the like. In someembodiments, the input device 2610 may provide a dedicated or primaryfunction, including, for example, a power button, volume buttons, homebuttons, scroll wheels, and camera buttons.

The device 2600 may also include one or more sensors 2620, such as aforce sensor, a capacitive sensor, an accelerometer, a barometer, agyroscope, a proximity sensor, a light sensor, or the like. The sensors2620 may be operably coupled to processing circuitry. In someembodiments, the sensors 2620 may detect deformation and/or changes inconfiguration of the electronic device and be operably coupled toprocessing circuitry which controls the display based on the sensorsignals. In some implementations, output from the sensors 2620 is usedto reconfigure the display output to correspond to an orientation orfolded/unfolded configuration or state of the device. Example sensors2620 for this purpose include accelerometers, gyroscopes, magnetometers,and other similar types of position/orientation sensing devices. Inaddition, the sensors 2620 may include a microphone, acoustic sensor,light sensor, optical facial recognition sensor, or other types ofsensing device.

In some embodiments, the electronic device 2600 includes one or moreoutput devices 2612 configured to provide output to a user. The outputdevice may include display 2614 that renders visual informationgenerated by the processor 2604. The output device may also include oneor more speakers to provide audio output.

The display 2614 may include a liquid-crystal display (LCD),light-emitting diode, organic light-emitting diode (OLED) display, anactive layer organic light emitting diode (AMOLED) display, organicelectroluminescent (EL) display, electrophoretic ink display, or thelike. If the display 2614 is a liquid-crystal display or anelectrophoretic ink display, the display may also include a backlightcomponent that can be controlled to provide variable levels of displaybrightness. If the display 2614 is an organic light-emitting diode ororganic electroluminescent type display, the brightness of the display2614 may be controlled by modifying the electrical signals that areprovided to display elements. In addition, information regardingconfiguration and/or orientation of the electronic device may be used tocontrol the output of the display as described with respect to inputdevices 2610.

The display may be configured to bend or fold along a flexible orbendable region of a foldable electronic device. The display may includeor be integrated with various layers, including, for example, a displayelement layer, display electrode layers, a touch sensor layer, a forcesensing layer, and the like, each of which may be formed using flexiblesubstrates. For example, a flexible substrate may comprise a polymerhaving sufficient flexibility to allow bending or folding of the displaylayer. Suitable polymer materials include, but are not limited to, vinylpolymers (e.g., polypropylene), polyester (e.g., polyethyleneterephthalate (PET), biaxially-oriented PET, and polyethylene napthalate(PEN)), polyimide, polyetherimide, polyaryletherketone (e.g., polyetherether ketone (PEEK)), fluoropolymers and copolymers thereof. Metallizedpolymer films, such Mylar®, may also provide flexible substrates.

The electronic device 2600 may also include a communication port 2616that is configured to transmit and/or receive signals or electricalcommunication from an external or separate device. The communicationport 2616 may be configured to couple to an external device via a cable,adaptor, or other type of electrical connector. In some embodiments, thecommunication port 2616 may be used to couple the electronic device to ahost computer.

The electronic device may also include at least one accessory 2618, suchas a camera, a flash for the camera, or other such device. The cameramay be connected to other parts of the electronic device such as thecontrol circuitry.

The foregoing description, for purposes of explanation, used specificnomenclature to provide a thorough understanding of the describedembodiments. However, it will be apparent to one skilled in the art thatthe specific details are not required in order to practice the describedembodiments. Thus, the foregoing descriptions of the specificembodiments described herein are presented for purposes of illustrationand description. They are not intended to be exhaustive or to limit theembodiments to the precise forms disclosed. It will be apparent to oneof ordinary skill in the art that many modifications and variations arepossible in view of the above teachings.

What is claimed is:
 1. An electronic device comprising: a flexibledisplay layer; and a cover layer coupled to the flexible display layerand comprising a foldable portion, the foldable portion configured to bemoved between: a folded configuration defining a fold having an exteriorregion and an interior region; an unfolded configuration; and anintermediate configuration between the folded configuration and theunfolded configuration, wherein: the exterior region has a first stresslevel in the unfolded configuration and a second stress level in theintermediate configuration, a magnitude of the first stress level beinggreater than a magnitude of the second stress level; and the interiorregion has a third stress level in the unfolded configuration and afourth stress level in the intermediate configuration, a magnitude ofthe third stress level being greater than a magnitude of the fourthstress level.
 2. The electronic device of claim 1, wherein: the exteriorregion has a fifth stress level in the folded configuration and amagnitude of the fifth stress level is greater than the magnitude of thesecond stress level; and the interior region has a sixth stress level inthe folded configuration and a magnitude of the sixth stress level isgreater than the magnitude of the fourth stress level.
 3. The electronicdevice of claim 1, wherein each of the first, the second, the third, andthe fourth stress levels is a bending-induced stress level.
 4. Theelectronic device of claim 3, wherein: the foldable portion of the coverlayer is chemically strengthened; the interior region has a compressivestress level due to chemical strengthening; and a magnitude of thecompressive stress level due to the chemical strengthening is greaterthan the magnitude of the third stress level.
 5. The electronic deviceof claim 1, wherein the foldable portion of the cover layer comprises aglass.
 6. The electronic device of claim 1, wherein: the foldableportion is a first foldable portion; the folded configuration is a firstfolded configuration, the unfolded configuration is a first unfoldedconfiguration, and the intermediate configuration is a firstintermediate configuration; the fold is a first fold and the interiorregion of the first fold defines a first minimum radius of curvature;the cover layer further comprises a second foldable portion, the secondfoldable portion configured to be moved between a second foldedconfiguration, a second unfolded configuration, and a secondintermediate configuration; and the second folded configuration definesa second fold and an interior region of the second fold defines a secondminimum radius of curvature greater than the first minimum radius ofcurvature.
 7. The electronic device of claim 6, wherein: the exteriorregion of the first fold is located on a first face of the cover layer;and an exterior region of the second fold is located on the first faceof the cover layer.
 8. An electronic device comprising: a flexibledisplay layer; and a chemically strengthened cover layer coupled to theflexible display layer and comprising a foldable portion, the foldableportion configured to be moved between: a folded configuration defininga fold having an exterior region and an interior region; an unfoldedconfiguration; and an intermediate configuration between the foldedconfiguration and the unfolded configuration, wherein: the exteriorregion has a first compressive stress in the unfolded configuration anda second compressive stress, less than the first compressive stress, inthe intermediate configuration; and the interior region has a thirdcompressive stress, less than the first compressive stress, in theunfolded configuration and a fourth compressive stress, greater than thethird compressive stress, in the intermediate configuration.
 9. Theelectronic device of claim 8, wherein the exterior region and theinterior region are symmetrically chemically strengthened.
 10. Theelectronic device of claim 9, wherein a depth of a first ion-exchangedlayer of the exterior region is equal to a depth of a secondion-exchanged layer of the interior region.
 11. The electronic device ofclaim 8, wherein: a stress state of the exterior region in the foldedconfiguration includes a chemical strengthening-induced compressivestress component and a bending-induced tensile stress component; and amagnitude of the chemical strengthening-induced compressive stresscomponent is greater than a magnitude of the bending-induced tensilestress component.
 12. The electronic device of claim 8, wherein: astress state of the interior region in the unfolded configurationincludes a chemical strengthening-induced compressive stress componentand a bending-induced tensile stress component; a magnitude of thechemical strengthening-induced compressive stress component is greaterthan a magnitude of the bending-induced tensile stress component; andthe third compressive stress is a sum of the chemicalstrengthening-induced compressive stress component and thebending-induced tensile stress component.
 13. The electronic device ofclaim 8, wherein the foldable portion of the chemically strengthenedcover layer comprises a glass or a glass ceramic.
 14. The electronicdevice of claim 8, wherein the foldable portion of the chemicallystrengthened cover layer has a uniform thickness.
 15. An electronicdevice comprising: a flexible display layer; and a chemicallystrengthened cover layer coupled to the flexible display layer andcomprising a foldable portion, the foldable portion configured to bemoved between: a folded configuration defining a fold having an exteriorregion and an interior region; an unfolded configuration; and anintermediate configuration between the folded configuration and theunfolded configuration, wherein: the exterior region defines a firstcompressive stress in the unfolded configuration and a secondcompressive stress, less than the first compressive stress, in theintermediate configuration; the interior region defines a thirdcompressive stress in the unfolded configuration and a fourthcompressive stress, greater than the third compressive stress, in theintermediate configuration; and moving the chemically strengthened coverlayer from the intermediate configuration to the unfolded configurationinduces: compressive bending stresses in the exterior region; andtensile bending stresses in the interior region.
 16. The electronicdevice of claim 15, wherein: the interior region defines a first minimumradius of curvature in the folded configuration; the interior regiondefines a second minimum radius of curvature in the intermediateconfiguration; and the second minimum radius of curvature is greaterthan the first minimum radius of curvature.
 17. The electronic device ofclaim 16, wherein a ratio of the first minimum radius of curvature tothe second minimum radius of curvature is greater than or equal to 0.25and less than
 1. 18. The electronic device of claim 15, wherein: thefirst compressive stress is a first surface compressive stress; thesecond compressive stress is a second surface compressive stress; thethird compressive stress is a third surface compressive stress; and thefourth compressive stress is a fourth surface compressive stress. 19.The electronic device of claim 15, wherein a magnitude of a differencebetween the first compressive stress and the third compressive stress isgreater than a magnitude of a difference between the second compressivestress and the fourth compressive stress.
 20. The electronic device ofclaim 15, wherein the foldable portion of the chemically strengthenedcover layer comprises a silica-based glass.